1. Field of the Invention
The present invention generally relates to information transmission methods, mobile communications systems, mobile stations and base stations and, more particularly, to an information transmission method, a mobile communications system, a mobile station and a base station in which information is converted into identification data having a relatively small data size.
2. Description of the Related Art
For downstream transmission in a mobile communications system, i.e. data transmission from a base station to a mobile station, a technology known as high speed downlink packet access (HSDPA) is used for high-speed, large-volume downloading. A discussion on HSPDA underway in 3rd Generation Partnership Project (3GPP) is directed to changing of a modulation scheme and a Turbo coding rate in accordance with the quality of reception at a mobile station. In changing a modulation scheme and a Turbo coding rate, it is necessary for a base station to notify a mobile station of the modulation scheme and the Turbo coding rate to be used. Particularly, in adaptive modulation coding (AMC) in which a modulation scheme and a Turbo coding rate are adaptively changed, transmission (signaling) of information related to the modulation coding scheme from the base station to the mobile station occurs frequently.
3GPP Technical Report (TR) 25.858V1.0.0 “8 Associated Signaling” (hereinafter, referred to as reference 1) gives a description of the signaling. Information related to the modulation coding scheme includes transport-format and resource combination (TFRC).
FIG. 12 shows an example of TFRC list given in reference 1. The list is provided in a portion of reference 1 where uplink signaling is described. The list lists substantially the same information related to the modulation coding scheme transmitted from the base station to the mobile station in downlink signaling. The list lists combinations of a modulation scheme, a transport block set (TBS) size and the number of codes. The modulation scheme may be one of two digital modulation schemes including quadrature phase shift keying and (QPSK) and 16 quadrature amplitude modulation (QAM). A TBS size indicates the data size of a transport block (TrBlk) included in a frame multiplied by the number of blocks. That is, the TBS size indicates the data size of a frame. A TBS size is a parameter related to Turbo coding and is one type of information related to modulation coding scheme. It is assumed here that a multicode scheme, in which a plurality of channelization codes (spreading codes) are assigned to a mobile station, is used. The list lists the number of codes included in a multicode (in the illustration, the number of codes is 5).
For example, TFRC(1) includes parameters such that the modulation scheme=QPSK, the TBS size=1200 bit and the number of codes=5. In the case of TFRC6, the modulation scheme=16 QAM, the TBS size=7200 bit and the number of codes=5. Assuming that spreading factor (SF)=16 and one frame=2 ms, the data size per frame is 4800 bits when the modulation scheme=QPSK, 9600 bits when the modulation scheme=16 QAM. The turbo coding rate is 1/4 for TFRC(1), 1/2 for TFRC(2), 3/4 for TFRC(3), 1/2 for TFRC(4), 5/8 for TFRC(5) and 3/4 for TFRC(6). The information given above is not immediately available from the table of FIG. 12, though.
In transmitting the information (TFRC, according to reference 1) related to the modulation coding scheme from the base station to the mobile station, the information is converted into identification data having a small data size for transmission. The identification data corresponds to transport-format and resource related information (TFRI) of reference 1. The data size of TFRI is defined in reference 1 as follows.    Channelization code set: 7 bits    Modulation scheme: 1 bit    Transport block set size: 6 bits
A channelization code set is a combination of a plurality of channelization codes assigned to a mobile station according to a multicode scheme. FIG. 12, listing TFRCs, would not be complete without listing channelization code sets instead of only the number of codes. FIG. 12, however, serves the purpose since it corresponds to a special case where the number of codes is fixed to 5. Therefore, only the number of codes is given.
Traffic between the base station and the mobile station is reduced by employing an information transmission method in which the information related to the modulation coding scheme is converted into the identification data.
The smaller the data size of the identification data, the smaller the traffic. Therefore, identification data having an even smaller data size is desired.